I am doing a simulation of flow in porous media and came into a problem. Someone suggest me to make the water slightly compressible. I worked on it for several days but still can not make it. Could anyone help me on it? What settings I need to do to make the water slightly compressible in CFX? Many thanks for your help.

Why do you think slightly compressible water will help? Is it likely that the density change is going to be significant? If not then I guarantee it will not help. Your problem is just obtaining convergence.

But compressible water is easy. Get the bulk modulus from google or somewhere, and define density as a function of pressure. I have done it many times and it works fine. And this is not a simplification, you are actually adding more physics to your model so your model will get more accurate - if compressibility is important.

Thank you so much for your reply. I set the "Heat Transfer" of fluid model to "Total Energy" and defined the water density as "( 997 / (1 - (Absolute Pressure - 101325 [Pa] ) / 2.04e9 [Pa] )) [kg m^-3]". Moreover, a minimum absolute pressure of 1000Pa and a maximum one of 1e6 Pa are set in "Table Generation". However, the model can not work at all. No information is given, even no error code. Could you please help me to figure out the problem in compressibilty setting or is there any other experience of it? Thank you for your kind help.

I am doing a model of water flowing over a porous medium, with mesh deformation in the water domain. The model can run without mesh deformation in water domain, but can not work with the mesh deformation. Others have suggested to make the water slightly compressible to solve the problem.

I have run the incompressible model. It can run without mesh deformation of water domain, but can not work with mesh deformation. That's why I would like to try the compressible model. How can I make the porous domain work together with the moving mesh water domain?

Please describe more details of the case. Total Energy with compressible water is the correct approach to resolve acoustic waves in water (e.g. water hammer), but it's not clear that this is what you want to do. If your timescale is small enough to resolve acoustic waves generated by a moving boundary then this might be a valid approach.